Comment #7 on issue 987 by dziamid: Not compatible with Linux x86 GCC3 http://code.google.com/p/gears/issues/detail?id=987
Here is a solusion that helped me:Install package 'xul-ext-gears'. Then go to /home/your_name/.mothilla/firefox/nonesense_name_folder and delete the following files: extensions.cache, extensions.ini, extensions.rdf. Now restart firefox and google gears should be there and detectable.
